The present invention relates to a fuel injection system for supplying combustion chambers of a diesel engine with a supplementary fuel, such as light oil, before feeding a main fuel, e.g., alcohol.
While light oil is conventionally used for the fuel of a diesel engine, alcohol has recently been tried as a substitute for light oil. If alcohol, a synthetic product, were used in place of light oil, which is obtained from petroleum, then those natural resources could be conserved.
Unlike light oil, however, alcohol does not permit satisfactory compression ignition in the combustion chambers of the diesel engine. If alcohol is used as a main fuel for the diesel engine, therefore, light oil must be used as a supplementary fuel.
Disclosed in U.S. Pat. No. 4,481,921, for example, is a fuel injection system in which two kinds of fuels can be fed into the combustion chambers of a diesel engine. In this system, main and supplementary fuels delivered from a fuel injection pump and a supplementary fuel feed device, respectively, are supplied to fuel injection nozzles disposed individually in the combustion chambers of the engine. The supplementary fuel feed device includes a plunger which is reciprocated by the pressure of the main fuel delivered from the pump. The reciprocation of the plunger causes a pumping action to feed the supplementary fuel to the fuel injection nozzle.
In this supplementary fuel feed device, however, the stroke of the plunger is fixed, so that the quantity of supplementary fuel supplied to the nozzle with every stroke is constant. According to the prior art fuel injection system, therefore, it is impossible to control the supplementary fuel supply to the fuel injection nozzle in accordance with the operating state of the engine.